Tiny geometrical irregulatities in model imported from Rhino
If geometry is beyond recovery, but the shape of the object remains intact (like in your case), it can sometimes work to regenerate the object using a combination of the Remesh modifier (with as many levels your machine can handle), and then using the Decimate modifier to simplify the resulting mesh.

In more detail:


The Remesh modifier will approximate your geometry by fitting it to a grid of voxels and connecting them to reform the mesh - a technique which will only approximate your geometry, but can get quite close at high resolutions. The key part here is that once "remeshed", your object will have uniform detail everywhere.
The high level of detail on the resulting mesh will then need simplification (as big flat surfaces will have been created out of many polygons instead of just one or two), which can be achieved well using techniques posted in other answers to this question: using Limited dissolve on the mesh in Edit mode, or applying a Decimate modifier (which has a few more options, but can accomplish the same result).


Note that this strategy will require you to reapply materials, remake UV maps, seams, sharp edges, etc. and is thus to be used as a last resort, or as the first step in your workflow if you are going to perform these steps afterwards.